Why Does Weight Depend on Location?

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Homework Help Overview

The discussion revolves around the concept of weight and how it varies depending on location, particularly in relation to the vacuum height of mercury and the units used to express pressure. Participants explore the implications of using different measurement systems and the definitions of weight versus mass.

Discussion Character

  • Conceptual clarification, Assumption checking, Mixed

Approaches and Questions Raised

  • Participants question the definitions and conversions of units related to pressure and weight, including the use of kg, pounds, and Newtons. There is a focus on the implications of these units in different contexts, such as commercial and scientific usage.

Discussion Status

The conversation includes various perspectives on the definitions of weight and mass, with some participants offering clarifications on unit usage and the impact of location on weight measurements. There is an ongoing exploration of how different measurement systems handle these concepts, but no explicit consensus has been reached.

Contextual Notes

Participants note the ambiguity in the use of pounds as either mass or force in the American system, and the discussion touches on the legal and practical implications of weight measurements across different locations.

chito1
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Homework Statement
Vacuum height of mercury
Relevant Equations
Is the pressure in kg / cm2abs when the vacuum height of mercury is 36cmHg?
Is the pressure in kg / cm2abs when the vacuum height of mercury is 36inHg?
Is the pressure in kg / lb/ni2abs when the vacuum height of mercury is 36cmHg?
Is the pressure in kg / lb/ni2abs when the vacuum height of mercury is 36inHg?
Vacuum height of mercury
 
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Whaatt?

What's an ni2abs? Can you please define your units, and show the unit conversions that are probably involved? Thanks.
 
chito1 said:
Homework Statement:: Vacuum height of mercury
Relevant Equations:: Is the pressure in kg / cm2abs when the vacuum height of mercury is 36cmHg?
Is the pressure in kg / cm2abs when the vacuum height of mercury is 36inHg?
Is the pressure in kg / lb/ni2abs when the vacuum height of mercury is 36cmHg?
Is the pressure in kg / lb/ni2abs when the vacuum height of mercury is 36inHg?

Vacuum height of mercury
I assume ni2abs should be in2absolute.
kg / cm2 is not a pressure. You probably mean kg wt/ cm2. Metric units don't play fast and loose with masses and weights like the American system does.

Regardless of the units used for the height of the mercury, you can use whatever units you like for the pressure. It's just a matter of making the necessary conversions.

If you are asking what units you would use for pressure in order to avoid or minimise conversions, the answer depends on the units you have for the density of mercury. E.g. if that is given as 13.56 grams per cubic centimeter, then a height of y cm of mercury will exert a pressure 13.56y grams wt per sq cm, or 0.01356y kg wt/cm2.

If you have a specific case in mind, please post it.
 
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haruspex said:
Metric units don't play fast and loose with masses and weights like the American system does.
Then how come the metrics world quotes weight in kilos whereas the yankee system correctly uses pounds? :))
And no, no one says "I weigh 80 Newtons"!
 
rude man said:
Then how come the metrics world quotes weight in kilos whereas the yankee system correctly uses pounds? :))
And no, no one says "I weigh 80 Newtons"!
The "yankee system" is ambiguous about whether pounds means mass or force.

Legally, medically, for purposes of commerce and for purposes of how fat you are when you stand on a scale, pounds are units of mass. Most of the time when we yankees think about the pound, we think of it as a unit of force. One cannot be correct about how a unit is used if one is ambiguous about how that unit is used.

When we say that we "weigh 80 kilograms" that is entirely proper and is a claim about our mass. Even though your physics teacher will ding you for using the word "weight" to denote a mass. Your physics teacher is paid to teach you a jargon usage of the term. That does not preclude the correctness of other meanings.
 
jbriggs444 said:
When we say that we "weigh 80 kilograms" that is entirely proper and is a claim about our mass. Even though your physics teacher will ding you for using the word "weight" to denote a mass.
Weight depends on where you are.
If your "weight" is 80kg on Earth it is much less on the Moon. So on the moon your scales give you your incorrect mass. Your scales give you your mass on Earth only. Your "weight" should be denominated in Newtons, not kg.
 
rude man said:
Weight depends on where you are.
If your "weight" is 80kg on Earth it is much less on the Moon. So on the moon your scales give you your incorrect mass. Your scales give you your mass on Earth only. Your "weight" should be denominated in Newtons, not kg.
The "net weight" on a 16 ounce can of peas is 16 ounces regardless. At the equator. At the poles. In Death Valley. On Mount Everest, on the moon and in orbit. That "net weight" is a mass measurement. By law. Exactly as we would want. We would not want to buy and sell goods using a measurement that depends on location.

A Toledo scale will give you the same answer for all of those except, possibly, in orbit. "Honest weight, no springs".

A spring scale will also give you the same answer, provided it is valid for commercial use. Such a scale will have been properly calibrated to deliver correct mass measurements in the location where it is used.
 
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